Critically coupled high-Q plasmonic guided mode resonances in the visible

Area of Science:

• Plasmonics and Nanophotonics
• Materials Science and Engineering

Background:

• High-quality factor (Q factor) plasmonic resonances are crucial for light-matter interactions but are often limited by metal absorptive losses.
• Achieving narrow linewidths and high coupling efficiency simultaneously in plasmonic metasurfaces remains a significant challenge.

Purpose of the Study:

• To demonstrate a novel plasmonic metasurface design that overcomes intrinsic loss limitations in the visible spectrum.
• To achieve critical coupling between long-range surface-plasmon polaritons (LRSPPs) and guided-mode resonances (GMRs) for enhanced light-matter interactions.

Main Methods:

• Fabrication of an ultrathin silver film supporting LRSPPs coupled to a square lattice of Ag nanoparticles.
• Utilized coupled-mode theory and coupled-dipole simulations to analyze resonance behavior and loss mechanisms.
• Investigated the suppression of radiative leakage and resistive dissipation.

Main Results:

• Achieved a collective LRSPP-GMR with a Q factor of 361 and 99.8% coupling efficiency at 633 nm.
• Demonstrated tunable resonances with Q factors >100 across the visible spectrum (down to 558 nm).
• Obtained an optimized Purcell factor of ~5x10^21 m^-3, twice that of uncoupled SPP GMRs, indicating superior light-matter interaction enhancement.

Conclusions:

• The developed LRSPP-GMR metasurface reconciles loss channels, enabling ultranarrow and efficiently excited plasmonic resonances.
• This platform offers a straightforward route for applications requiring enhanced light-matter interactions, such as SERS, nonlinear optics, and sensing.
• The findings provide a new paradigm for designing high-performance plasmonic devices.